Technology of detecting a pitch of a note performed by a musical instrument in real time or a pitch of a person's voice has been developed and researched in order to extract performance information data on the note of the musical instrument or the person's voice or to play real-time music in concert.
Methods usually used to detect a pitch include a method of analyzing a frequency of a digital signal of a performing note or voice; a method of calculating a peak or zero-crossing period of a waveform in order to calculate a period of repetitive wave; and a method using the autocorrelation of a waveform.
In the frequency analysis method, an error in a high-frequency band is the same as an error in a low-frequency band. However, when the frequency analysis method is used to detect a pitch of sound produced by a musical instrument, the probability of a pitch detection failure due to an error increases in the low-frequency band in which a frequency interval between pitches is narrower than in the high-frequency band. In the method using autocorrelation, an error is large in the high-frequency band due to the characteristics of calculation.
In the method of calculating a peak or zero-crossing period, it is difficult to accurately calculate a period due to, for example, noise, and thus the result of the method is inaccurate.